Polymerizable compounds with at least one conjugated unsaturated group are widely used as basic chemicals. Examples are acrylic monomers, in particular acrylic acid and methacrylic acid as well as their esters. They are mostly used for the synthesis of polymers.
These polymerizable compounds, while being valuable starting materials for the preparation of a broad variety of synthetic materials, suffer from the drawback of their inherent activity, i.e. the fact that they are viable to undergo polymerization even at times where polymerization is not desired. Examples of such undesired polymerizations, which accordingly require inhibition, are purification processes, often involving high temperatures (such as distillation processes) as well as the synthesis of such starting materials, as already during synthesis a premature polymerization needs to be prevented in order to maintain high yield and efficiency of the synthetic procedure.
In the art there are already examples of inhibitors which may be employed under these circumstances.
For example, U.S. Pat. No. 2,715,101 A discloses the use of methylene blue (MB) for the stabilization of diacetylene or of mixtures containing diacetylene against polymerization. However, methylene blue has low solubility in a polymerizable compound with at least one conjugated unsaturated group, like acrylic acid or methacrylic acid or their esters.
A similar disclosure is given in EP 2053066 A1 as well as in U.S. Pat. No. 4,983,761.
MB, due to the presence of the chloride anion furthermore has proven to be corrosive. In order to reduce the content of this corrosive component, US 2006074257 A1 suggests replacing the chloride anion with other anionic groups, such as sulfates or acetates using for example ion exchange processes. However, those types of methylene blue derivatives have still low solubility. In addition, these compounds require a separate synthesis step including isolation steps, rendering the overall process of stabilizing the polymerizable compounds against premature polymerization laborious.